Determination of Fe2+ and Fe3+ in Aqueous Solutions Containing Food Chelators by Differential Pulse Anodic Stripping Voltammetry

The objective was to investigate interactions between iron and food chelators in an aqueous environment. The net complexation were investigated by DPASV in a NaClO₄ electrolyte using a platinum electrode. The experimental conditions were simulating the environment of the human duodenum. The results indicated a net coordination affinity between Fe²⁺ and the organic acids in the following order; ascorbic acid≈phytate>pyruvate>lactate>acetate. For Fe³⁺ net complexation, the stability was in the order of lactate>phytate>pyruvate>acetate>citrate. In conclusion, DPASV in conjunction with a platinum electrode is suitable for studies in aqueous systems where the net complexation of metal is important.     

Implementation and Evaluation of an Embedded LES-RANS Solver

In the current work, we present the development and application of an embedded large-eddy simulation (LES) - Reynolds-averaged Navier Stokes (RANS) solver. The novelty of the present work lies in fully embedding the LES region inside a global RANS region through an explicit coupling at the arbitrary mesh interfaces, exchanging flow and turbulence quantities. In particular, a digital filter method (DFM) extracting mean flow, turbulent kinetic energy and Reynolds stress profiles from the RANS region is used to provide meaningful turbulent fluctuations to the LES region. The framework is developed in the open-source computational fluid dynamics software OpenFOAM. The embedding approach is developed and validated by simulating a spatially developing turbulent channel flow. Thereafter, flow over a surface mounted spanwise-periodic vertical fence is simulated to demonstrate the importance of the DFM and the effect of the location of the RANS-LES interface. Mean and second-order statistics are compared with direct numerical simulation (DNS) data from the literature. Results indicate that feeding synthetic turbulence at the LES interface is essential to achieve good agreement for the mean flow quantities. However, in order to obtain a good match for the Reynolds stresses, the LES interface needs to be placed sufficiently far upstream, which in the present case was six spoiler heights before the fence. Further, a realistic spoiler configuration with finite-width in the spanwise direction and inclined at 30 degrees was simulated using the embedding approach. As opposed to the vertical fence case this is a genuinely (statistically) three-dimensional case and a very good match with mean and second-order statistics was obtained with the experimental data. Finally, in order to test the present solver for high sub-sonic speed flows the flow over an open cavity was simulated. A good match with reference data is obtained for mean and turbulence profile comparisons. Tones in the pressure spectra were predicted reasonably well and an overall sound pressure level with a maximum deviation of 2.6 d B was obtained with the present solver when compared with the experimental data.     

A Test Frame for Uniaxial Creep

Experimental Techniques -     

Transverse-momentum spectra in Au+Au and d+Au collisions at sqrt[s(NN)]=200 GeV and the pseudorapidity dependence of high-p(T) suppression

We present spectra of charged hadrons from Au+Au and d+Au collisions at sqrt[s(NN)]=200 GeV measured with the BRAHMS experiment at RHIC. The spectra for different collision centralities are compared to spectra from p+(-)p collisions at the same energy scaled by the number of binary collisions. The resulting ratios (nuclear modification factors) for central Au+Au collisions at eta=0 and eta=2.2 evidence a strong suppression in the high p(T) region (>2 GeV/c). In contrast, the d+Au nuclear modification factor (at eta=0) exhibits an enhancement of the high p(T) yields. These measurements indicate a high energy loss of the high p(T) particles in the medium created in the central Au+Au collisions. The lack of suppression in d+Au collisions makes it unlikely that initial state effects can explain the suppression in the central Au+Au collisions.     

Deuterium in vivo labelling of cytokinins in Arabidopsis thaliana analysed by capillary liquid chromatography/frit-fast atom bombardment mass spectrometry

A method was developed for analysing the biosynthetic rate of the cytokinin class of plant hormones. Transgenic, cytokinin-overproducing Arabidopsis thaliana plants were incubated in liquid culture media enriched with 30% deuterium oxide, and incorporation into the different parts of the cytokinin molecule was analysed by capillary liquid chromatography/frit-fast atom bombardment mass spectrometry after precolumn propionylation. The sugar moieties of the cytokinins generally showed a high and independent incorporation, so the analysis in this study focused on the cytokinin base moieties. It was observed that during a 24 h incubation period almost all labelling was incorporated into the side-chain, rather than the adenine moiety. The incorporation dynamics of isopentenyladenosine-5'-monophosphate, zeatinriboside-5'-monophosphate (ZRMP) and zeatin-9-glucoside were investigated through analysis of the cytokinin base fragments in high-resolution selective ion monitoring mode. Using a fractional synthetic rate approach, the biosynthetic rate of ZRMP was determined to be 18 ng h(-1) g(-1) fresh weight, giving a turnover time of 25 h. A method for the mass isotopomer abundance analysis of the cytokinins in the zeatin family, based on selective reaction monitoring, was also developed to gain further sensitivity. Use of this technique showed that there was a higher level of enrichment in zeatin nucleotide than in the corresponding nucleoside, in agreement with the hypothesis that cytokinin nucleotides are primary products in this pathway.     

Evolution of the nuclear modification factors with rapidity and centrality in d + Au collisions at (sqrt)[N(S)N]=200 GeV

We report on a study of the transverse momentum dependence of nuclear modification factors R(dAu) for charged hadrons produced in deuteron + gold collisions at sqrt[s(NN)]=200 GeV, as a function of collision centrality and of the pseudorapidity (eta=0, 1, 2.2, 3.2) of the produced hadrons. We find a significant and systematic decrease of R(dAu) with increasing rapidity. The midrapidity enhancement and the forward rapidity suppression are more pronounced in central collisions relative to peripheral collisions. These results are relevant to the study of the possible onset of gluon saturation at energies reached at BNL RHIC.     

Binding affinities in the SAMPL3 trypsin and host–guest blind tests estimated with the MM/PBSA and LIE methods

We have estimated affinities for the binding of 34 ligands to trypsin and nine guest molecules to three different hosts in the SAMPL3 blind challenge, using the MM/PBSA, MM/GBSA, LIE, continuum LIE, and Glide score methods. For the trypsin challenge, none of the methods were able to accurately predict the experimental results. For the MM/GB(PB)SA and LIE methods, the rankings were essentially random and the mean absolute deviations were much worse than a null hypothesis giving the same affinity to all ligand. Glide scoring gave a Kendall's τ index better than random, but the ranking is still only mediocre, τ = 0.2. However, the range of affinities is small and most of the pairs of ligands have an experimental affinity difference that is not statistically significant. Removing those pairs improves the ranking metric to 0.4-1.0 for all methods except CLIE. Half of the trypsin ligands were non-binders according to the binding assay. The LIE methods could not separate the inactive ligands from the active ones better than a random guess, whereas MM/GBSA and MM/PBSA were slightly better than random (area under the receiver-operating-characteristic curve, AUC = 0.65-0.68), and Glide scoring was even better (AUC = 0.79). For the first host, MM/GBSA and MM/PBSA reproduce the experimental ranking fairly good, with τ = 0.6 and 0.5, respectively, whereas the Glide scoring was considerably worse, with a τ = 0.4, highlighting that the success of the methods is system-dependent.     

Vibrational entropy of dislocations in Al

The region nearest to a lattice defect must be described by an atomistic model, while a continuum model suffices further away from the defect. We study such a separation into two regions for an edge dislocation. In particular we focus on the excess defect energy and vibrational entropy, when the dislocation core is described by a cluster of about 500–100?atoms, embedded in a large discrete and relaxed, but static, lattice. The interaction between the atoms is given by a potential of the embedded-atom model type referring to Al. The dynamic matrix of the vibrations in the cluster is fully diagonalized. The excess entropy ΔS near the core has positive and negative contributions, depending on the sign of the local strain. Typically, ΔS/k _B ≈ 2 per atomic repeat length along the dislocation core in fcc Al. In the elastic continuum region far from the dislocation core the excess entropy shows the same logarithmic divergence as the elastic energy. Although the work refers to a specific material and defect type, the results are of a generic nature.